1. Field of the Invention
The present invention relates to cutting tools used on milling machines for machining a workpiece, and particularly to a cutting tool composed of a side cutter oriented transversely to the rotational axis of the milling machine spindle for performing contour machining operations in three dimensions.
2. Description of the Prior Art
Milling machines are in widespread use for machining metal workpieces into a finished metal product. Machining operations of this type range from simple straight cuts and bores to forming complex three dimensional contours. Milling machines are divided into horizontal and vertical types depending on the orientation of the spindle axis. Common to all milling machines is a bed to which is connected a workholder and at least one column for supporting a spindle head. The spindle head contains the spindle and drive for the spindle, and is movable in relation to the workholder. The workpiece is affixed to the workholder and a cutting tool is connected with the spindle. The cutting tool is rotated by the spindle drive and is brought into contact with the workpiece by movement of the spindle head.
In the case of machining contours in three dimensions, typically many passes are made by a cutting tool in a progressive fashion over the area being contoured. FIGS. 1 and 1A show a typical state of the art milling operation in which a spindle 20 turns an end mill cutter 22 which makes a series of groove cuts 24 to form a contour 26 on a workpiece 28. Due to the complexity of the movements of the cutter to achieve the desired contour, use of Computer Numerical Control (CNC) systems are now becoming the standard to control movement of the cutting tool in relation to the workpiece. In CNC, a programmer converts movements of the cutting tool into a digital sequence which is then fed into a computer. The computer is linked electronically to the drives for three dimensional movement of the spindle head and the spindle drive. A computer program converts the digital data into electronic commands that regulate the feed and speed rates.
The milling operation just described suffers from a number of drawbacks. The large number of passes of the end mill cutter results in an extensive amount of time required to complete a contouring operation on a workpiece. Further, the workpiece comes into contact with only a portion of the cutting edge of the end mill cutter as each groove cut is made. This is because the end mill is rotating about an axis which moves laterally with respect to the workpiece. Accordingly, the cutting edge of the end mill does not directly engage the workpiece in the direction of feed, resulting in inefficient cutting. Still further, a second machining operation is required to smooth-out the grooves cuts.
As further examples of milling machines, the following U.S. patents are of interest.
U.S. Pat. No. 1,029,402 to Ritter, dated June 11, 1912, discloses a milling tool attachment for a drill press. Bevel gears connected with the spindle drive a gear set that in turn drives a side cutter oriented perpendicular with respect to the axis of rotation of the spindle. The resulting milling tool attachment has only a vertical axis of movement, and is not suited for use in three dimensional contour milling.
U.S. Pat. No. 1,040,954 to Johnson, dated Oct. 8, 1912, discloses an attachment for milling machines which enables quick change of cutters and supports various forms and shapes of cutters. The attachment is composed of a U-shaped casing for supporting the cutter and associated gearing which permits turning of the cutter in a direction parallel with respect to the spindle of the machine.
U.S. Pat. No. 2,963,944 to Strauss, dated Dec. 13, 1960, discloses a milling machine which may be converted to various orientations of the axis of rotation of the spindle. In this device, the upper portion of the base carries a turret which carries the spindle and its drive. The turret is rotatable and a separately powered vertical head is employed for vertical and angular milling.
U.S. Pat. No. 4,993,138 to Yang, dated Feb. 19, 1991, discloses a milling machine having a grooved overarm horizontally disposed in relation to the machine body. A vertical milling attachment slides along the grooved overarm for horizontal movement.
While the milling machine art is extremely well developed, there yet remains the need for a milling machine cutter tool which is structured and oriented so as to perform complex three dimensional contour machining operations and which further provides for the cutting edges of the cutter to engage the workpiece in the same direction as the feed direction, thereby resulting in maximal cutting efficiency.